The present invention relates to a cylinder of a short stroke having a guide in which the guide is provided in a piston.
In the case of a cylinder of a short stroke slidably accommodating a piston in a piston chamber, a piston rod is supported by a bearing or the like so that the piston is prevented from being inclined and the piston can slide smoothly.
However, if the bearing is provided, there are problems that a height (axial length) of the cylinder can not be suppressed to a low level, and if the bearing which suppresses the height of the cylinder to the low level, the piston rod is inclined and a sliding surface is scratched by scoring.
It is an object of the present invention to provide a thin cylinder (of a short stroke) having a guide in which a height of a cylinder can be suppressed to a low level, there is no scoring, and inclination and rotation of a piston are prevented.
It is another object of the invention to provide a cylinder having a guide having a simple structure and capable of preventing a piston from being inclined.
To achieve the above objects, the present invention provides a cylinder having a guide, including a cylinder body provided therein with a piston chamber surrounded by a side wall, a rod-side end wall and a head-side end wall, and a piston slidably accommodated in the piston chamber, wherein the piston comprises a piston body which is air-tightly slides in the piston chamber by action of fluid pressure, a piston rod extending from a central portion of the piston body and passing through the rod-side end wall and projecting outside of the cylinder body, and a guide hole formed in central portions of the piston body and the piston rod, the head-side end wall of the cylinder body includes a guide shaft extending from a central portion of an inner surface of the head-side end wall into the piston chamber and fitted into the guide hole, a plurality of sets of grooves are formed at positions at which an inner surface of the guide hole and an outer surface of the guide shaft are opposed such as to be located at positions which are symmetric with respect to a point of a center of the guide shaft, and a plurality of steel balls are interposed between the grooves such that the steel balls can roll.
In this cylinder having the above structure, if pressure fluid is supplied to or discharged from the piston chamber, the piston slides in the vertical direction in the cylinder, but at that time, the piston is guided by the guide shaft provided in the piston and thus, the piston is not inclined.
Further, the piston is guided through the plurality of steel balls provided in the plurality of grooves extending in the axial direction of the piston and the guide shaft, and the guide shaft is fixedly formed at the head-side end wall and does not move. Therefore, the piston can slide in the axial direction but can not turn.
The steel balls roll in the grooves extending in the axial direction of the piston and the guide shaft as the piston slides. Therefore, the piston slides smoothly, and no scoring is generated when the piston slides.
Since the guide shaft is provided in the piston, the height of the cylinder can be suppressed to a lower level and thus, the cylinder can be made thin, and the pressure receiving area of the piston can be made wide.
Therefore, if the cylinder having the guide of the present invention is used as a power source for an air chuck or a rotary actuator, since the cylinder is thin, the air chuck or the rotary actuator can be reduced in size. Since the pressure receiving area of the piston is wide, a great driving force can be obtained although its size is small. Since the piston slides only in the axial direction and does not rotate, its action is correct.
According to one of embodiments of the present invention, the guide shaft includes pins at opposite ends of each of the grooves for preventing the steel balls from falling out.
According to another embodiment, a side wall of the cylinder body and the rod-side end wall are formed as one piece, the head-side end wall and the guide shaft are formed as one piece and connected to the side wall.
The cylinder of the present invention can be formed as a double-acting cylinder or a single-acting cylinder. When the single-acting cylinder is employed, the cylinder has two pressure chambers divided by the piston body, one of the chamber is connected to a supply port, a return spring is provided in the other chamber such that the return spring repels the piston body at a position separated away from the piston rod.
The cylinder having the guide of the invention, a chuck mechanism, a turning table or the like can be added, and the cylinder can be used as a power source for the air chuck or the rotary actuator. In this case, since the cylinder is thin, the air chuck or the rotary actuator can be reduced in size. Since the pressure receiving area of the piston is wide, a great driving force can be obtained although its size is small. Since the piston slides only in the axial direction and does not rotate, its action is correct.
When the chuck mechanism is added to the cylinder of the invention, the chuck mechanism includes guide means fixed on the cylinder body, a plurality of jaw members which are opened and closed along the guide means, and a link mechanism connected to the jaw members and the piston rod for converting a forward and a backward motion of the piston rod into an opening and closing motion of the jaw members.
When the turning table is added to the cylinder of the invention, the turning table is mounted on the cylinder body such that the turning table can rotate around a center axis of the piston, and a converting mechanism for converting a forward and a backward motion of the piston into a rotational motion of the turning table is connected to the turning table and the piston.
The converting mechanism is constituted by a plurality of thread grooves formed in an inner peripheral surface of the hole into which the piston rod of the central portion of the turning table is fitted, and a plurality of sliding elements projected from a side surface of the piston rod and fitted to one of the thread grooves.